The present invention relates to a piezoelectric speaker, and more particularly to a structure of a piezoelectric speaker in which a piezoelectric film is molded into a corrugate shape to form a vibrating diaphragm, and alternating signals are inputted into electrodes formed on the vibrating diaphragm to thereby generate sound wave.
A conventional speaker such as a Heil speaker or a ribbon speaker in which a thin film is molded into a corrugate shape and electrodes are formed to complete a vibrating diaphragm has been proposed. In the Heil speaker or ribbon speaker, both vertical ends in the vibrating diaphragm molded into a corrugate shape are fixed to a frame when the vibrating diaphragm is to be fixed to the frame. Both side ends that are wavy are not fixed and kept free. Since the electrodes formed on each crest and trough of the vibrating diaphragm are connected in series, the flowing current is also caused to flow through the electrodes connected in series.
FIG. 1 is a perspective view of a conventional piezoelectric speaker. In the corrugate shaped molded vibrating diaphragm 1, after the vertical ends 3-1 have been bonded to the vertical frames 2-1 and 2-2, the wavy side ends 4 are fixed to side frames 6-1 and 6-2 by adhesives 5. Also, electrode lead terminals 8-1 and 8-2 deposited on piezoelectric films 7-1 and 7-2 and external lead lines 9-1 and 9-2 are screw-fastened together to the vertical frames 2-1 and 2-2 of plastics by means of bolts 10-1 and 10-2. The acoustic signal current is inputted into the electrode lead terminals 8-1 and 8-2 from the external lead lines 9-1 and 9-2.
Accordingly, the current for driving the vibrating diaphragm 1 is inputted concentratedly from first ends of the narrow thin lead electrode terminals 8-1 and 8-2. However, since the electrodes 11 formed in the crests and troughs are connected in parallel, this system is different in electrode structure from the above-described Heil speaker or ribbon speaker.
However, if there would be no misunderstanding the representation of the numeral, only the main reference numeral will be used to collectively represent the components. This is the case also in other components that will be described hereunder. This rule will be applied to the components in the same manner.
However, since the above-described piezoelectric films 7 have a large static capacitance, if the frequency is increased, an impedance is lowered so that a large alternating current will flow. On the other hand, since the electrodes are manufactured by means of a thin coating method such as deposition, as shown in FIG. 1, all the signal applied to the electrodes is inputted from the electrode lead terminals 8-1 and 8-2 at first ends of the electrode leads 12-1 and 12-2 on the extension lines of the electrodes 11. For this reason, a large amount of current is caused to flow into the thin narrow electrode lead terminals 8-1 and 8-2. The electrode lead terminals 8-1 and 8-2 are evaporated to cause a breakdown of lines.
Also, as another problem, in order to generate a sufficient sound pressure in the piezoelectric speaker, the output voltage of an amplifier has to be further stepped up to apply a high voltage. Although it is not necessary to provide the voltage in the several kVs like a static speaker, since the peak voltage reaches about 100V even in the piezoelectric speaker, if the user""s hand would touch the electrodes 11, the side frames 6-1 and 6-2, the vertical frames 2-1 and 2-2 and the like as shown in FIG. 1, there would be an electric accident.
Also, the conventional structure in which the vibrating diaphragm 1 formed by the piezoelectric film into the corrugate shape is fixed to the frame shown in FIG. 1 suffers from a problem that, if the sound pressure is somewhat increased, the vibrating diaphragm 1 is vibrated in universal directions to generate a busy sound at a predetermined frequency to generate noise.
Accordingly, an object of the present invention is to provide a piezoelectric speaker in which a breakdown of an electric lead terminal is prevented when a large amount current is caused flow into a thin narrow electrode lead terminal, any electric accident may be prevented in an electrode and a frame that would be likely to be touched by hands, the precision of position and shape of the electrode formed by using a mask is enhanced, and the generation of busy sound that becomes noise may be prevented even at a predetermined frequency of the vibrating diaphragm.
In order to attain the above objects, according to the present invention, there is provided a piezoelectric speaker comprising a vibrating diaphragm 1 formed by two piezoelectric films 7-1, 7-2 being put together and made in a bimorph type, and formed into a corrugate shape as the whole to have crests 16-1 and troughs 16-2 alternately and to have walls 17 which connect the crests 16-1 and the troughs 16-2 and structured such that side ends 4-1, 4-2 corresponding to the right and left ends of the vibrating diaphragm 1 are attached to side frames 6-1, 6-2 placed at the right and the left of the vibrating diaphragm 1 and one longitudinal end 3-1 and the other longitudinal end 3-2 of the vibrating diaphragm 1 are attached to vertical frames 2-1, 2-2 disposed between the right and left side frames 6-1, 6-2 and that electrodes 11-1, 11-2 are formed on the vibrating diaphragm 1 to generate sound waves by alternate signals being input to the electrodes 11-1, 11-2, wherein each of the right and left side frames 6-1, 6-2 fixing the right and left side ends 4-1, 4-2 of the vibrating diaphragm 1 is sectioned into an upper plate 19-1 and a lower plate 19-2 by the right side end 4-1 or the left side end 4-2 of the vibrating diaphragm 1 formed in the corrugate shape as the whole, and a vibrating diaphragm supporting portion 31 of the upper plate 19-1 and a vibrating diaphragm supporting portion 32 of the lower plate 19-2 are formed in the same corrugate shape as the corrugate shape of the side ends 4-1, 4-2 of the vibrating diaphragm 1 so that the side ends 4-1, 4-2 of the vibrating diaphragm supporting portion 31 of the upper plate 19-1 and the vibrating diaphragm supporting portion 32 of the lower plate 19-2 in the state of the corrugate shape of the vibrating diaphragm 1 being maintained.
According to this structure, the side ends 4-1, 4-2 of the vibrating diaphragm 1 formed into a corrugate shape are clamped by the pair of upper and lower plates 19-1, 19-2 the vibrating diaphragm supporting portions of which are formed in the corrugate shape, to form the side frames 6, 6-1, 6-2, and the electrodes 11-1, 11-2 formed on the surface of the vibrating diaphragm 1 are connected at a plurality of positions by conductive leads 20 mounted on the side frames 6-1, 6-2 to output.
Accordingly, it is possible to firmly fix the vibrating diaphragm 1 to the side frames 6-1, 6-2 and to prevent the current from concentrating on a local part of the thin electrode lead terminals 8-1, 8-2.
Furthermore, in the piezoelectric speaker according to the present invention, the vibrating diaphragm 1 is clamped by the upper plate 19-1 and the lower plate 19-2 in such a way that the side ends 4-1, 4-2 of the vibrating diaphragm 1 project from the side frames 6-1, 6-2, electrode leads 12-1, 12-2 are formed on projections 23 so projected, and the electrode leads 12-1, 12-2 are connected by the leads 20.
With such an arrangement, the side ends 4-1, 4-2 of the vibrating diaphragm 1 are fixed to the frame so as to project from the side frames 6-1, 6-2 composed of the pair of the upper and lower clamping plates 19-1, 19-2 and the electrode leads 12-1, 12-2 formed on the projecting projections 23 are attached to the leads 20 connected to the side frames 6-1, 6-2.
Accordingly, it is possible to readily and firmly connect the electrodes 11-1, 11-2 and the leads 20 with each other without any adverse affect to the vibrating surface at a plurality of positions.
In the piezoelectric speaker according to the present invention, a plurality of electrodes 11, 11-1, 11-2 are formed on the same surface of the vibrating diaphragm 1, electrodes 11, 11-1, 11-2 that are not in conductive communication with each other on the same surface are provided within the plurality of electrodes 11, 11-1, 11-2, and the electrodes 11, 11-1, 11-2 are electrically conductive by the lead 20.
According to the above-described arrangement, the pattern is made as shown in FIG. 3, instead of the insulative strip portion of the mask shown in FIG. 2, to thereby prevent the bends and displacement of the insulative portion. Then, the electrode leads 12, 12-1, 12-2 formed on the piezoelectric films 7, 7-1, 7-2 have disconnected portions on the midway and are not contiguous to the electrode lead terminals 8-1, 8-2. However, according to the invention of the first aspect, the respective electrodes 11, 11-1, 11-2 mounted on the side frames 6, 6-1, 6-2 are connected.
Accordingly, it is possible to enhance the positional precision of the electrodes 11, 11-1, 11-2 and to attain the prevention of the breakdown of the electrode lead terminals 8-1 and 8-2 at once.
Furthermore, in the piezoelectric speaker according to the present invention, partitioning plates 26-1, 26-2 are inserted between the two side frames 6-1, 6-2, and the crests 16-1 and the troughs 16-1 of the vibrating diaphragm 1 are partitioned by the partitioning plates 26-1, 26-2.
With such an arrangement, when the vibrating diaphragm 1 is vibrated while receiving the acoustic signal, the partitioning plates 26-1, 26-2 are inserted between the two side frames 6-1, 6-2 in order to prevent the lateral displacement or to prevent the resonance caused by the mutual affect of adjacent units of the crests 16-1 and troughs 16-2.
Accordingly, it is possible to prevent the user""s finger from touching the vibrating diaphragm 1 by the partitioning plates 26-1, 26-2 to thereby serve as the sufficient countermeasure to the electrical accident and thus it is possible to solve the two different problems of the electrical accident and a buzz sound at a time.
Further, in the piezoelectric speaker according to the present invention, the partitioning plates 26-1, 26-2 are formed integrally with the side frames 6-1, 6-2.
Accordingly, it is possible to enhance precision in arrangement of the partitioning plates 26-1, 26-2, and at the same time to simplify the work for mounting the partitioning plates 26-1, 26-2 to the frames to thereby make it possible to reduce the cost.
Furthermore, in the piezoelectric speaker according to the present invention, the respective vertical frames 2-1, 2-2 on one side and the other side are divided into upper vertical frames 2-1-A, 2-2-A and lower vertical frames 2-1-B, 2-2-B, the respective upper plates 19-1 of the side frames 6-1, 6-2 are assembled between the upper vertical frame 2-1-A on one side and the upper vertical plate 2-2-A on the other side at the right and the left to constitute a frame plate 29-1, the respective lower plates 19-2 of the side frames 6-1, 6-2 are assembled between the lower vertical frame 2-1-B on one side and the lower vertical plate 2-2-B on the other side at the right and the left to constitute a frame plate 29-2, and the vibrating diaphragm 1 is fixed to the frame plates 29-1, 29-2 under the condition that tension in the direction towards the side ends, i.e. in the right-and-left direction is kept applied.
Accordingly, it is possible to maintain the tension of the vibrating diaphragm 1 for a long period of time, to readily assemble, and to prevent the generation of a buzz sound.
Furthermore, in the piezoelectric speaker according to the present invention, the vertical frames 2-1, 2-2 are formed to be longer than the length of the vibrating diaphragm 1 in the right-and-left direction located between the two side frames 6-1, 6-2 and tension in the right-and-left direction is applied to the vibrating diaphragm 1 when the vertical frames 2-1, 2-2 are mounted on the side frames 6-1, 6-2 to assemble the frame.
With such an arrangement, the vibrating diaphragm 1 is first fixed to the side frames 6-1, 6-2, and at this time, the vertical frames 2-1, 2-2 that are longer than the length in the right-and-left direction of the vibrating diaphragm 1 between the pair of side frames 6-1, 6-2 are inserted in between the side frames 6-1, 6-2 so that the vibrating diaphragm 1 is fixed to the frame under the condition that the tension in the right-and-left direction is kept.
Accordingly, the vibrating diaphragm 1 is firmly fixed to the side frames 6-1, 6-2 by the pair of side plates 19-1, 19-2 whereby the manufacturing work is facilitated the generation of the buzz sound is prevented.